Completed Projects: Facts about Antibiotics in Animals and their Impact on Resistance (FAAIR)


Ecological and Human Health Consequences




  • Exposure to antimicrobials fundamentally alters microbial ecosystems of humans, animals and the environment, which may lead to the development of antimicrobial resistance.
  • Increasing antimicrobial resistance limits treatment options, raises health care costs, and increases the number, severity and duration of infections.
  • Antimicrobial use is a major cause of antimicrobial resistance.
  • It is estimated that, in the United States, the amount of antimicrobials administered to food animals is comparable to that used in humans. These antimicrobials are utilized largely to promote growth and prevent disease, thereby reducing production costs. A substantial amount of them are sold over-the-counter and do not require a veterinarian's prescription.
  • Most antimicrobials used in food animal production are the same as, or closely related to, drugs used in human medicine.
  • Current antimicrobial use policy for animals in the US differs from policy enacted in the European Union, which has banned the use of some antimicrobials for growth promotion on the farm.
  • Also of concern is the farm use of antimicrobials of critical importance in human medicine, such as fluoroquinolones and third (or higher) generation cephalosporins.
  • Once the prevalence of antimicrobial resistance in a population reaches a certain level, reversal of the problem becomes extremely difficult.

The Risk to Human Health

Since the 1940s, antimicrobials have been considered the gold standard for treatment of bacterial infections in both animals and humans. Taken properly, these medications may destroy or disable the bacterial pathogens that cause infections. In recent years, however, we have witnessed a rapid increase in drug-resistant bacteria leading to failure in the treatment of infectious diseases.

The overuse of antimicrobials in food animal production is an under-appreciated problem. In both human and veterinary medicine, the risk of developing resistance rises each time bacteria are exposed to antimicrobials. Resistance opens the door to treatment failure for even the most common pathogens and leads to an increasing number of infections. The mounting evidence of the relationship between antimicrobial use in animal husbandry and the increase in bacterial resistance in humans has prompted several reviews of agricultural practices by scientific authorities in a number of countries, including the US.

Selected Report Findings

  • Most food animals in the US are exposed to antimicrobials in feed, water, or by injection at some point during their lives. 
  • Fecal waste from food animals treated with antimicrobials, which is often composted and spread as fertilizer, is implicated in environmental contamination with resistant bacteria.
  • Several lines of evidence may link antimicrobial use in food animal production to resistant infections in humans. These include: (i) direct studies tracing resistant infections in humans to specific meat and poultry operations; (ii) temporal evidence (i.e. the emergence of resistance in animal-associated bacteria prior to its emergence in human pathogens); (iii) circumstantial evidence linking human disease to trends in resistance among common bacterial pathogens such as Salmonella, Campylobacterand E. coli; (iv) studies suggesting that farmers and family members may be more likely than the general public to harbor antimicrobial-resistant intestinal bacteria; and (v) studies of the transfer of resistance in commensal bacteria.
  • Published risk assessments of antimicrobial use in agriculture likely underestimate the risk to human health because they tend to ignore future cumulative effects, ecological impact and potential transfer of resistance from one bacterium to another and from one animal species to another.

Selected Conclusions

  • All uses of antimicrobials in animals, agriculture and humans contribute to the global pool of antimicrobial resistance genes in the environment.
  • Use of antimicrobials in food animals contributes to the growing problem of antimicrobial resistance in human infections. Transfer of bacteria from food animals to humans is a common occurrence.
  • The amount of antimicrobials administered to animals is comparable to that used in humans. Unlike use in humans, however, much of the antimicrobial administration to food animals is to large groups at low doses, for non-therapeutic purposes such as growth promotion and disease prevention.
  • The elimination of non-therapeutic use of antimicrobials in food animals and agriculture will lower the burden of antimicrobial resistance in the environment with consequent benefits to human and animal health.

Selected Recommendations

Based on its assessment of the scientific evidence, the Scientific Advisory Panel strongly urges implementation of policy reforms in a timely fashion. Specific changes called for are: 

  • Antimicrobial agents should not be used in agriculture in the absence of disease.
  • Use of antimicrobials in food animal production should be limited to therapy for diseased animals or prevention of disease when it has been documented in a herd or flock.
  • Use of antimicrobials for economic purposes such as growth promotion or to enhance feed efficiency should be discontinued (with the exception of ionophores and coccidiostats, because current evidence indicates that use of these antimicrobials does not affect resistance in human pathogens).
  • Because of their critical importance to treat human disease, fluoroquinolones and third generation (or higher) cephalosporins should not be used in agriculture except to treat refractory infections in individual animals.
  • Antimicrobials should be administered to animals only when prescribed by a veterinarian.
  • In many cases, legislation by Congress or direct changes in policy by the US Food and Drug Administration, US Department of Agriculture, US Environmental Protection Agency, or other government agencies will be necessary to implement the recommendations of the Panel. The ecology of antibiotic resistance should be considered by regulatory agencies in assessing human health risk associated with antibiotic use in agriculture.

Other FAAIR Materials: (all links below should be active links to tertiary pages. 

FAAIR Scientific Advisory Panel

Michael Barza, M.D. (co-chair), Professor, Tufts University School of Medicine, Boston, MA; Director of Medicine, Carney Hospital, Boston, MA
Sherwood Gorbach, M.D. (co-chair), Professor, Tufts University School of Medicine, Boston, MA; Attending Physician, New England Medical Center, Boston, MA
John Bailar, III, M.D., Ph.D., Professor Emeritus, Department of Health Studies, University of Chicago, Chicago, IL
Paula J. Fedorka-Cray, Ph.D., Research Leader-- Antimicrobial Resistance Research Unit, USDA-ARS-Richard B. Russell Agricultural Research Center, Athens, GA
Scott McEwen, D.V.M., D.V.Sc., Diplomate ACVP, Professor, Department of Population Medicine, University of Guelph, Guelph, Ontario
Thomas F. O’Brien, M.D., Medical Director of Microbiology, Brigham and Women’s Hospital, Boston, MA; Associate Professor of Medicine, Harvard Medical School, Boston, MA
Anne O. Summers, Ph.D., Professor, Department of Microbiology, University of Georgia, Athens, GA
Morton Swartz, M.D., Professor, Harvard Medical School, Boston, MA; Chief of Jackson Firm of the Medical Service, Massachusetts General Hospital, Boston, MA
Anne Vidaver, Ph.D., Professor, Department of Plant Pathology, University of Nebraska, Lincoln, NE

Complete list of references cited  

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